The invention relates to an improvement in the liquid phase hydrogenation of coal utilizing an ebullated bed reactor.
The liquid phase hydrogenation of coal in an oil slurry under upflow ebullated bed reaction conditions is disclosed by Keith, et al in U.S. Pat. No. 3,519,555.
U.S. Pat. No. 3,540,955 to Wolk, et al, the disclosure of which is incorporated herein, discloses an improved process for the hydrogenation of coal wherein the composition of the liquid within the reactor is optimized by controlling the amount of liquid residuum and solids therein by removing a portion of the solids from the high residuum concentration liquid effluent prior to recycle to the reactor. The liquid residuum content of the liquid slurry within the reactor is preferably maintained in a range from about 30-45 weight percent and unconverted processed solids are maintained in amounts between about 10-25 weight percent. The aforementioned optimization is accomplished in accordance with this prior art method by flashing the liquid reactor effluent in a depressurization step to remove a gaseous component which includes unreacted hydrogen and light hydrocarbons, followed by a liquid solid separation step which is performed on the remaining high viscosity liquid stream. A stream of reduced solids concentration and residuum is then recycled back to the reaction zone for further hydrogenation and to maintain the concentration of residuum and solids within the desirable range.
Under this prior art process, the liquid solids separation step must inherently be performed at low pressures and reduced temperatures in comparison with the operating conditions in the reaction zone. Such low pressures and temperatures make removal of fine ash and unconverted coal solids from the liquid reactor effluent quite difficult because of the high viscosity of the effluent. In addition to the aforementioned disadvantages, the liquid with reduced solids content must be repressurized prior to returning to the reaction zone thereby increasing the overall costs of the process. The present invention obviates the foregoing difficulties.